Many organizations maintain heterogeneous systems of information technology infrastructure comprising assorted data formats originating from multiple sources. For example, an organization may use a data warehouse to manage structured data and a map-reduce engine to manage semi-structured or unstructured data. Data warehouses may provide tools to extract, transform, and load data (“ETL tools”). Some ETL tools permit a user to specify operations that process data from multiple sources or to perform other functions. Such a tool may include a graphical user interface (“GUI”) that displays a model of the entities and data sources involved in an ETL process.